Signal strength control of a system usually requires a variable gain/attenuation element. A variable attenuator is desirable in situations that need to handle higher amount of power.
Passive elements in an variable attenuator may grouped into two kinds—(i) one includes series elements that connect parallel to the direction of the input terminal to output terminal, and (ii) the second includes shunt elements that connect from the input, the output, or the intersection points of two series elements to the ground (earth).
An attenuator may have lower attenuation when its series elements have smaller impedance and its shunt elements have higher impedance. At such a setting, the input signal may be isolated from ground by high impedance shunt elements and traveling through low impedance series elements from input to output. On the other hand, an attenuator may have higher attenuation when its series elements have larger impedance and its shunt elements have lower impedance. At such setting, the input signal may be diverted to ground through low impedance shunt elements, and only a small portion of input signal may travel through the high impedance series elements to the output.
MOSFETs can be used in a conventional configuration to provide tunable passive elements in an attenuator. However, the impedance of a MOSFET varies significantly with the strength of input signals it carries, thereby degrade its gain linearity. Thus, there is a need for linearization systems and methods for variable attenuators.